Colon cancer is the second leading cause of cancer deaths in the United States, with over 100,000 new cases and over 55,000 deaths expected in 2005. Traditionally, the colon surface is examined using colonoscopy, which involves the use of a lit, flexible fiberoptic or video endoscope to detect small lumps on the colon surface called polyps. Polyps are known to be precursors to colon cancer. Although colonoscopy provides a precise means of colon examination, it is an invasive procedure. Thus, colonoscopy is associated with a significant risk of injury to the colon and the possibility of colon perforation and peritonitis, which can be fatal.
A less invasive alternative to traditional colonoscopy is Computed Tomographic Colonography (CTC). CTC makes use of 2-dimensional images generated by computed tomography (CT) imaging systems, as well as 3-dimensional computer graphics renditions of the colonic surface using these images. A drawback of CTC is that radiologists must examine hundreds of 2-d images and/or 3-d renditions to detect polyps, which is very time consuming and can lead to inaccurate diagnoses.
Three-dimensional surface images rendered from an internal perspective (“virtual fly-through” or “virtual colonoscopy”) appear similar to those produced by conventional colonoscopy. However, navigation through a tortuous, complex structure like the colon is challenging and, frequently, portions of the colonic surface may be missed, leading to incomplete examinations. Cylindrical and planar map projections have been proposed to increase the viewable surface during fly-through, but the presentation format is unfamiliar and the physician may still not have a complete view. Thus, there is a need in the art for methods of identifying polyps using CTC that are less time consuming, allow for more complete examination of the colonic surface, and allow for greater ease of identification of polyps than current methods.